Copyright 2021 Optical Sensors Sweden AB
Why measure visibility?
Fog makes a lot of activities hazardous.
Accidents because of fog occur in many cases like:
Road traffic
- serial collisions
- at landing and starting of airplanes and helicopters
Sea transports
- ship collisions

We will here describe a few examples on how measurement of visibility increases the safety in different cases.

Fog warning at highways
Visibility measurement is often a part of a road weather system RWS. The information is for example used for warning trafficants and for setting speed limits in order to reduce the risk for accidents.

Variable signs
The optimal light intensity of the LED's in a variable traffic sign varies with the light conditions but also with the visibility. During foggy conditions - at night time as well as daytime - the intensity should be increased when fog is present in order to make them more visible. The fog detecting can be done using a visibility sensor like our OFS or MiniOFS.

Turning on street lightning at daytime during fog
In foggy conditions at daytime the safety can be increased by turning the street lighting on. The trafficants will then get information that they will not get otherwise like an indication of the visibility by counting how many lamps that can be seen and also the location of the road side and the road.

Giving landing permission to helicopters
Landing a helicopter (as well as flying in one) in foggy conditions is dangerous. (In many cases flying is not allowed unless the ground can be seen from the helicopter)
Therefore visibility sensors are sometimes installed at helicopter landing pads. Then landing will only be permitted if the visibility is better than a certain value. Good visibility is in the same way important for drones.

At big airports the visibility is measured regularly since start and landing in poor visibility conditions is much more complicated than at good visibility conditions (or forbidden).

Sea transports
In earlier years fog was considered as a major risk factor for all sea transports. Today when radar is almost standard the problems because of fog at open sea are small.
But in harbors, channels and rivers where many ships are located in small areas fog is still a problem when it occurs. Therefore visibility sensors are installed in some shop routes. There is also some interest for installing visibility sensors on board. The bridge staff wants to know how large portion of the radar screen that is also visible with the eyes...